1) You can still choose 1920x1080 on the 1440p monitor for a game so that is a non-issue.
(also the SIZE won't affect frame rate, only the chosen RESOLUTION.)
I play many most games at 1920x1080 on my GTX680. At 2560x1440 I play Torchlight, CIV5, Mass Effect 3, Diablo 3 etc. Most shooters I'm at 1920x1080.
2) Some games look far, far better at 2560x1440 such as CIV5 (anything with small text/HUD elements). Also the extra 3" of the 27" is very significant.
3) ROG SWIFT has G-Sync which I don't believe the other monitor has. That can make games much, much smoother. You will need a supported NVidia card to use that feature though.
Summary:
Cost difference aside the SWIFT is an amazing monitor so I recommend it.